Peter Frost's anthropology blog, with special reference to sexual selection and the evolution of skin, hair, and eye pigmentation

Saturday, January 14, 2012

African Americans and recent evolution

Fulani woman, Nigeria. Source.African Americans aren’t just sub-Saharan Africans with European admixture. There has also been admixture from Amerindian peoples and from groups partly of North African origin, like the Fulani.

Have African Americans evolved since they first came to North America? The question may seem strange. Doesn’t evolution happen over millions of years? The first slaves disembarked in the future United States back in 1619 and the last ones arrived (illegally) in the 1850s. That’s about three centuries. How could any population evolve over so short a time?

Yet natural selection can cause significant change in as little as eight generations, at least in nonhuman species. In humans, it has altered at least 7% of the genome over the last 40 thousand years, and most of that change has happened over the last 10 thousand years (Hawks et al., 2007).

Jin et al. (2011) argue that African Americans have changed genetically over the last three centuries, not only through European admixture but also because of natural selection. First, many black slaves died during their passage from Africa to the New World. The survivors, already a select group, faced a new environment in colonial America. They had to adapt to new challenges in their struggle for existence, such as new pathogens, new social structures, and new means of subsistence.

To identify these effects of natural selection, Jin et al. (2011) used two methods on a large sample of African Americans (5,210 individuals). They first looked at various genomic regions to see whether the degree of European admixture was higher or lower than the admixture for the genome as a whole, estimated at 21.61%. Such deviations would be “signals” of natural selection favoring certain genetic variants at the expense of others.

The second method involved comparing the African component of the African American genome with the genomes of present-day sub-Saharan African populations—in proportion to their respective contributions to the African American gene pool.

And the results? Some genomic regions did deviate from the level of 21.61% European admixture. Many of them were associated with diseases, like prostate cancer and hypertension, that are more common among African Americans than among Euro Americans. Alleles that protect against malaria were also less frequent than would be predicted by European admixture. This is evidence that natural selection has been eliminating alleles that are less necessary in North America.

These results seem expectable. Too expectable, in fact. Yes, prostate cancer occurs more often in African Americans than in Africans, but this difference is due to underreporting and shorter life expectancy in Africa. Keep in mind that prostate cancer tends to be diagnosed late in life (Ogunbiyi & Shittu, 1999; Osegbe, 1997).

There are other grounds for skepticism. The deviations from overall European admixture were small, less than 2.6%. Admittedly, the sample size was large, so sampling error couldn’t be responsible. But there may have been other sources of error.

One of them concerns the estimated European admixture of 21.61%. This figure is consistent with previous estimates and is probably the best one available. But the degree of admixture varies among African Americans, especially by social class and by geographic region.

The authors also oversimplify their model when they describe African Americans as sub-Saharan Africans with European admixture. There has also been Amerindian admixture, as noted by Myrdal (1944, p. 124):

Indians were held as slaves in some of the American colonies while Negro slaves were being imported. Equality of social status between Indians and Negroes favored intermingling. The whites had little interest in hindering it. As the number of Negro slaves increased, the Indians slaves gradually disappeared into the larger Negro population. Whole tribes of Indians became untraceably lost in the Negro population of the South. […] Twenty-seven and three-tenths per cent of the Negro sample of 1,551 individuals examined by Herskovits claimed some Indian ancestry.

The authors state that they excluded African American individuals who had more than 2% Native American/East Asian ancestry, but such exclusion is at best approximate. And what about the many individuals with 1-2% Amerindian ancestry?

Another wild card is North African admixture. The Atlantic slave trade involved some populations that were partly of Arab/Berber descent, such as the Fulani (also known as Fulbe or Peul. The hotel maid who gave DSK a BJ was a Fulani). To some degree, North African admixture would resemble European admixture. To some degree, it would have its own characteristics.

Admittedly, these other admixtures were relatively small. But one doesn’t need a big factor to explain a deviation of two percent or so.

Ideas for future research

I’d like to see more research on recent evolution among African Americans, in particular on the possibility of gene-culture co-evolution. One cultural determinant of genetic change might be Christianity, specifically the way it has structured family life, turned men into active fathers, and created a strict rules-based culture.

Briefly put, I’d like answers to the following questions:

1. Was natural increase higher among church-going African Americans than among non-churchgoers? (because of a higher rate of family formation, stronger male involvement in the family, lower rate of infant mortality, etc.)

2. Did churchgoers have a different psychological profile than non-churchgoers? In other words, were non-churchgoers disproportionately made up of individuals who had trouble complying with a rules-based culture?

3. Did the higher natural increase of churchgoers, together with their psychological profile, lead to an evolutionary process similar to what Clark (2007) has described for England? (i.e., gradual demographic replacement of impulsive, present-oriented individuals with disciplined, future-oriented individuals).

4. Did this process abort in the 1960s with the decline in church life among African Americans?

References

Clark, G. (2007). A Farewell to Alms. A Brief Economic History of the World, Princeton University Press, Princeton and Oxford.

16 comments:

"4. Did this process abort in the 1960s with the decline in church life among African Americans?"

There's one particular aspect to this part which i wonder about which is the extreme weirdness of an enclosed underclass environment where most people are on welfare.

Some of the characteristics most people may not know

1) extreme terriotoriality. they don't like moving off their patch and the borders are violently enforced by gangs. each housing project or equivalent is mostly a little island

2) most of the women have children with multiple men and each child is liable to have more than one possible father. popular males will have numerous unacknowledged children. what this means is there's very little certainty over who is related to who. combined with (1) this leads to a great deal of inbreeding through ignorance including (potentially a lot of) half-siblings

3) welfare means males don't need to support their offspring and so compete for females in other ways. one successful method is simply using violence and intimidation to drive off male competitors

4) the people with the most anti-social traits tend to have children the earliest (15-16 ish)so the generations are whizzing by

Peter, this is slightly off-topic, but maybe can be researched in future posts regarding complexion preferences (lighter/darker).

I know you've made posts stating that men prefer light-skinned women. Then why is tanning so popular? If we look at popular shows such as "Jersey Shore" the women go to extra lengths to look tanned in order to be beautiful. Conversely, describing a woman as "pasty" (i.e. pale) is usually seen as derogatory. Is there some contradiction here? Just something I've been thinking about in terms of beauty standards.

(Sorry for hijacking the post, maybe this is an idea for future posts.) Thanks

You wrote a couple posts back in 2009 and 2010 that, looking back, were extremely profound. They were about the fact that men outnumber women at all reproductive ages due to improved infant mortality and liberalized divorce laws.

This one fact, that men outnumber women, got lost in the argument over the ramifications for society.

Especially in light of another article by Nicholas Eberstadt (saying what we've all heard before) I think those facts need a re-airing because most people do not know them.

It would illuminate so much and help many come to better grips over why things are the way they are and plan accordingly.

One real consequence is that many men hate women and some even think they are evil because of their despondency over not being able to find a woman or are surprised at how much they must lower their standards.

"They first looked at various genomic regions to see whether the degree of European admixture was higher or lower than the admixture for the genome as a whole"

The European admixture early on was often from white women -female indentured servants, transported convicts prostitues, female vagrants, wives and daughters of Irish and other rebels soldiers- who were given to black slaves. Also the African male slaves were, especially in the west Indies, selected (ie for desirable characteristics) see'To Hell Or Barbados'. So it is likely that for men the more docile/intelligent but strong and hard working slave got to reproduce. Could this increase the "Church-going African Americans" by selection for placidity?

In the later period it was white slaveholders and overseers who would be impregnating female slaves. Don't know if that made a difference.

Malaria was once common in North America although I have read that slaveowners avoided exposing slaves to it - they were too valuable. Virtually all men get 'prostrate cancer', if they live long enough but these are often slow growing cancers which are best left alone, or so I've read. (There are types of 'breast cancer' which are relatively inert)

I know you've made posts stating that men prefer light-skinned women. Then why is tanning so popular? If we look at popular shows such as "Jersey Shore" the women go to extra lengths to look tanned in order to be beautiful.

Humans seem to prefer skins which are both more of a golden component as well as lighter:

""There are two main pigments that affect the yellowness of skin. One comes from carotenoids, the other from melanin, which is yellow and dark, giving the brown colour that we associate with a sun tan. Using a scientific instrument called a spectrophotometer, I measured the colour change associated with changes in carotenoid levels and melanin levels in the skin. Then, using a computer programme, I allowed participants to adjust the levels of carotenoid and melanin colour in photographs of faces to make them look as attractive as possible. Participants chose to increase melanin colour slightly, but increased carotenoid colour lots."

"Any gender differences? "The preference for light skin is stronger in women's faces than in men's."

for images (for me the White face with lower melanin and higher carotenoid seem like it has the obviously most attractive, and "whitest" complexion).

It seems like tans are mainly driven by preference for skin with a more yellow tone, more than darkness. When adjusting for yellowness, Whites barely seem to have a preference for skin darker than their own (there is barely a shift).

Makes sense - tanning is about being orange and bronzing, not about being blackened.

However, even if Whites don't prefer skin darker than the average when adjusting for yellowness, it is an interesting question why they don't prefer skins lighter than the average, when this preference, for both lightness and yellowness is evident in say, the Black people in the sample above. I think that probably is a combination of cultural effect and sex difference related confound.

In the absence of cultural restraints (e.g., religion), all humans seem to shift toward shorter-term and less stable sexual relationships, as well as less paternal investment.

This is a point where religious conservatives agree with the HBD community. Religious conservatives, however, think that this shift in sexual behavior is potentially the same in all human populations. Unfortunately, it isn't.

We see this in many immigrant groups. During the first generation, their families are more stable than those of the majority. But as they assimilate into the majority culture, where restraints on sexual behavior are much weaker, we see a complete reversal.

Steve Sailer thinks the problem is that many immigrants are assimilating to African American norms of behavior. My analysis is a bit diffferent from his.

Reader,

I don't believe that men necessarily prefer lighter-skinned women. I believe that lighter female skin has an effect on male sexuality that is culturally promoted in traditional societies. It seems to reduce male aggressiveness and promote feelings of care and tenderness, much like the feelings one has toward an infant (which likewise has lighter skin).

Even before the tanning fad took off in the 1920s, there was some fascination with dark female skin. The "dark lady" was seen as the object of a stronger, even more violent erotic desire. We find this "dark lady" motif even in the folk traditions of European peoples that had no contact with black Africans.

This is a subject I'd eventually like to investigate under controlled conditions.

Hiawatha,

It's going to get worse before it gets better. Over the past half-century, we've been deregulating the marriage market in the naive belief that people will be free to exit unhappy relationships and enter happier relationships.

There has instead been an intensification of male-male competition for younger women. A surplus of older women is piling up in older age brackets and a corresponding surplus of younger men is piling up in younger brackets.

In addition, through better health care, the male-biased sex ratio at birth has been progressively extended into older age groups. It's now somewhere in the 50-60 age bracket in most developed countries.

Finally, there's the growing impact of sex-selective abortions.

Eventually, we'll have to provide financial incentives for women to have girl babies. Yeah, I know. That would be "playing God." But what have we been playing all this time?

Sean,

I'm not sure about your comment that white women were given to black slaves. There may have been such cases. But the main reason was that there were initially no State-enforced restrictions on mixed marriages.

Matt,

Ruddier faces project an image of strength (the same is true for browner faces). But strength is not a quality that men generally seek in women. At least, it's not in the top ten.

On Hiawatha's point about the male/female ratios, I second his request to re-examine this issue in a series of new posts, if possible, especially if there's any new information or data that has come out recently. The last posts on this were made in 2009. Many people are interested in this topic.

David Buss, the famous evolutionary researcher, wrote in his book "The Evolution of Desire" (2003), "As men mature into their 30s and 40s, the sex ratio typically tilts in their favor, if they have survived the risks." This statement by Buss is no longer true, and needs to be corrected. Men are continuing to face an uphill battle even into their 40s, based on my observations.

Additionally, multiple researchers are writing articles about how "men are the winners in today's sexual marketplace" and how the women need our sympathy and support, when that is completely false. A notable voice in this debate is Mark Regnerus, a researcher from the University of Texas, who's written several well-publicized articles in the media about this.

In this Slate.com article, he claims, "Sex is cheap... Life for young men just isn't so bad." He makes it sound as if there is no shortage of women at all. This article has received a lot of publicity.

It's become fashionable to sympathize with women's ostensible "difficulty" in dating when in fact the exact opposite is happening, it's the men who are having difficulty right now, but no one is writing about that.

In this recent New York Times article, the authors are once again lamenting women's "predicament", which is completely false:

"this shift in sexual behavior is potentially the same in all human populations. Unfortunately, it isn't...Steve Sailer thinks the problem is that many immigrants are assimilating to African American norms of behavior."

It's a mixture imo. One of the interesting things about this is the relatively newly created white underclass in places where the factories used to be. They, like a lot of 2nd generation immigrants ape African-American culture but only up to the limit of their genetics.

For example if there was a very specific type of violent behavior caused by a gene which had a frequency of 6% among African-American males, 3% among a migrant group and 1% among another group then all three groups might all equally copy the culture of the first but only up to the point where the knife goes in. At that point the ratio drops to 6/3/1.

A lot of the copying is due to fear of the 6% too, "pick a weaker target" type behavior.

The other thing you notice though because it started from a lower base is what at least appears to be a very rapid de-evolution among the white underclass. If a frequency of some trait - like a particular kind of lethally impulsive violence - goes up from 6% to 7% you notice it less than when a frequency of 1% doubles to 2%.

Part of the problem is historical inertia. Back in the 1960s, there were indeed too many women and too few men. Today, our chattering classes are dominated by people who came of age during that period. Another thing: the losers in the current mate market are young White men. Such people are not normally framed as "victims."

One thing I've noticed is that religion still has some restraining power on most Americans, whether black or white. Here in Quebec, and in England, religion seems to have disappeared entirely for 95% of the population. While the result has been a rise in dysfunctional sexual behavior and male violence, the increase is not really comparable to what we see elsewhere, such as in African American communities in the U.S. and North African communities in France.

"One thing I've noticed is that religion still has some restraining power"

Yes, very true.

"a rise in dysfunctional sexual behavior and male violence, the increase is not really comparable to what we see elsewhere"

Yes that's what i meant by 6% to 7% versus 1% to 2%. The increase is more noticeable because it's from a much lower base and even though the new level is still much lower.

In particular there's a very specific characteristic that tends to stand out - the absence of normal levels of hesitation and restraint when using potentially lethal violence.

This is a characteristic feature of certain areas - it's not really it just seems that way because it is the characteristic feature of the dominant males - and to be honest 30 years ago when i first came across it i thought it was just a black thing with a few white exceptions. However it seems to be becoming more common among the white underclass now as well - although still at a much lower frequency - so now i wonder about specific genes.

"It's going to get worse before it gets better. Over the past half-century, we've been deregulating the marriage market in the naive belief that people will be free to exit unhappy relationships and enter happier relationships."

This also allows people to defect from their agreements to their advantage and their former partners disadvantage (especially to men's disadvantage in the Western world).

Thus you would expect a similar situation to the prisoners dilemma occurring where people are less likely to mate cooperatively and instead try to screw the other over first.

Hence you would see a shift from long-term mating strategies to short-term strategies where it is harder to reproductively exploit the other mating partner.

In fact this propensity to defect from agreements to your advantage and the other persons disadvantage is why we have contract law. Without prohibitions against this sort of behaviour, no one would cooperate in the marketplace.

It's surprising that the people who drafted the family/marriage laws/policies weren't able to see that this is what would occur from the implementation of those laws/policies. Hell, this line of reasoning is used to justify the existence of contract law in all law degrees, (which is generally the sort of background education you would expect law and policy makers to have).

Welcome to my blog! For the most part, this page will be an extension of my website, with comments relating to my research. But it will also branch out into more general discussions of human evolution.